Vivax malaria more deadly than thought, say scientists

A common form of malaria that is endemic across swathes of Asia, and Central and South America may be far deadlier than thought, according to new research.

Plasmodium vivax has long been associated with a high economic burden because of loss of working hours and need for treatment — but rarely with death.

Now a two-year study, presented at the annual meeting of the American Society of Tropical Medicine and Hygiene (ASTMH) last week (4–8 December), has found that P. vivax was responsible for about a third of 66 malaria-related deaths at Karitas Hospital in eastern Indonesia.

Kevin Baird, lead author of the study and director of the Eijkman-Oxford Clinical Research Unit in Indonesia, told SciDev.Net that this is further proof that P. falciparum, the form of malaria common in Africa,is not the only one with high death rates.

The view that most malaria deaths are caused by P. falciparum is "pure fantasy", he said. "If P. vivax is causing deaths, as the data suggest, we need to look at areas where it is endemic and rethink our malaria strategy."

Baird found that the two forms of the disease were responsible for an equal proportion of 3,449 malaria-related hospital admissions, a pattern he is confident would be similar across India, Pakistan and South-East Asia.

Although P. falciparum was more likely to cause severe symptoms, such as unconsciousness and anaemia, once the patient was ill enough to require intensive care P. vivax was just as likely to kill, the study found. It also caused a higher proportion of deaths in adults.

Baird said P. vivax has had a long history of misdiagnosis, and the real picture has emerged only since the development of accurate diagnostics that can distinguish between both forms of the disease. "People are beginning to take notice of P. vivax as a serious threat," he said.

He noted that work presented at the ASTMH meeting, such as a refined version of a map locating global malaria hotspots, showed that progress is being made. But more research needs to be done, he added. One problem is how to stop a genetic mutation, common to people in the region, from interfering with the use of primaquine — the only drug capable of fighting P. vivax effectively.

Julian Rayner, group leader of the malaria programme at the Wellcome Trust Sanger Institute, in the United Kingdom, agreed. "Now is the time to put more resources into fighting P. vivax," he said.

But Mark Rowland, deputy director of the Malaria Centre at the London School of Hygiene and Tropical Medicine, said: "This might be a particularly virulent localised strain but it is not the norm elsewhere.

"Certainly P. vivax mortality has been underestimated, but it is still nothing compared with P. falciparum."

The study is in press at the American Journal of Tropical Medicine & Hygiene.